"With such a large number of users unaware that apps can drain their data it does raise concern that many consumers will find themselves facing unnecessarily large mobile bills," Rebtel CEO Andreas Bernstrom says.

Stockholm and Luxembourg-based Rebtel, like Skype, provides voice-over-Internet (VoIP) mobile calls, which is an inexpensive way around high mobile calling charges. I think VoIP count against data (does it?), so you can see why Rebtel is looking into this - as customers learn they are paying for app usage, they might trade off by using VoIP less. Or that sort of thing.

Mobile Entertainment writes that "90 percent of respondents said data played a big part in choosing their phone contracts, though 23.1 percent say they didn't know app usage can swallow their allowance, and 15.7 percent said they were unsure."

The potential for that to deliver a monthly blow to paying customers is growing now that cellphone carriers are moving away from "all you can eat" packages with the advent of 4G networks, Bernstrom notes. 4G networks support a much bigger feast of apps and services than do earlier mobile networks like 3G.